Electric rheostat.



PATENTED OCT. 13, 1903.

No. 741,207. I

L. WILSON. ELECTRIC RHBOSTAT.

APP LIUATION FILED APR. 6, 1903.

.NO MO'DEL.

1N VEN TOR.

WITNESSES ATTORNEY.

UNITED STATES Patented October 13, 1903.

PATENT OEEIcE.

LEONARD WILSON, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO STANLEY ELECTRIC MANUFACTURING COMPANY, OF PITTSFIELD, MASSACHUSETTS, A CORPORATION OF NEW JERSEY.

ELECTRIIC RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 741,207, dated October 13, 1903.

Application filed April 6, 1903. Serial No. 151,231. (No model.)

To aZZ whom it may concern: Be it known that I, LEONARD WILSON,

subject of the King of England, and a resident of Pittsfield, Massachusetts, have invented certain new and useful Improvements in Electric Rheostats, of which the following is a specification.

The object of my invention is to provide a rheostat which shall allow the current passing through any electrical apparatus or circuit to be varied gradually from zero to a maximum, which shall be simple and cheap in construction, and which shall be economical in operation.

My invention consists in the arrangement hereinafter described, whereby parts of a rheostat may be connected in series and in shunt with a circuit and their values varied in such manner as to achieve the objects set forth above.

Referring to the drawings, Figure 1 shows diagrammatically an arrangement embodying my inventionfaud Fig. 2 shows a similar arrangement dilfering in details in the construction of the rheostat.

The drawings show my invention applied to the field of a separately-excited generator; but it will be understood that my invention is equally applicable to other electrical apparatus in which it is desirable that the current be gradually and economically varied between wide limits.

In Fig. l, A represents the armature, and B the field of a separately-excited generator.

C C are the exciter bus-bars.

D and E are resistances connected at suit able intervals tocontact-buttons d d", 850., and e 6 &c., respectively.

F is a rotatable switch-arm pivoted at G, adapted tov engage the contact-buttons. It carries on its under side a stud II.

I is a pivoted switch-blade adapted to be engaged by stud H and by it thrown into and out of contact with contact J by the passage of arms F.

K is a stop for arm F.

L is a switch for opening the rheostat-circuit.

Switch-blade I is connected to a point a near the middle of resistance E. Contact J is connected to one end of resistance D.

The operation is as follows: Suppose the voltage between bus-bars C C to be one hundred and the values of the resistance of field B and of the resistances D and F to be each twenty ohms. Then starting with the arm F in the position shown in Fig. 1 field B is connected directly across the bus-bars C C, and the maximum currentviz., five amperes will be passing through field B. Now as arm F is moved along contacts 6 6 &c., resistance E is gradually inserted in series with field B until when arm F is on contact c all of E is in series. The resistance of the circuit is new forty ohms, and the current through field B is two and one-half amperes. Now as arm F is moved from c to 01 switch-blade I is moved into contact with contact J. Field B is now in parallel circuit with resistance D, and the part of resistance E between 6 and e is in series with the parallel circuit. If this part is one-half of E, the resistance of the circuit is now twenty ohms and the current is five amperes; but as field B is shunted by a resistance equal to itself it is traversed by a current of two and one-halfamperes. Therefore under the conditions stated no change in the current through field B occurs when arm F is moved from c to (1 In practice, however, I prefer to make the resistance between 6 and e a little greater than half of E, thus obtaining a slight drop in the current through field B proportionate to the reduction of the other steps. Now as arm F moves along contacts (1 (W, &c., the resistanceshunting field B is gradually diminished, while the resistance in series with field B is gradually increased until when arm F is on contact d field B is short-circuited, and no current flows through it.

' Fig. 2 differs from Fig. 1 only in that pivoted switch I and contact J in Fig. 1 are replaced by concentric contact-strips I and J in Fig. 2, while the circuit is closed by contact H, which is carried by arm F and which replaces the stud H in Fig. 1. Contact II is insulated from arm F. The operation is in all respects the same as in Fig. 1.

While for the purpose of this explanation I have selected values of the resistances D and E equal to each other and to the resistance of field B, it is obvious that such equality is not necessary for the purposes of my invention, but that the relative values of the resistances and the number of contacts may be varied to best suit varying conditions of control. Accordingly I do not desire to limit myself to the particular construction and arrangementof parts here shown, since changes therein which do not depart from the spirit of my invention will be obvious to those skilled in the art.

Having thus fully described my invention, what I claim as new, and desire to protect by Letters Patent, is

1. In an electric rheostat, two sets of resistances, a series of contacts connected to said resistances, a movable switch-arm adapted to engage said contacts, and a switch connecting the end of one set of resistances to a point near the middle of the other set and adapted to be operated by the movement of said movable arm.

2. In an electric rheostat, two sets of resistances, a circular row of contacts connected to said resistances, a rotary switch-arm adapted to engage said contacts, and a switch connecting the end of one set of resistances to a point near the middle of the other set and adapted to be operated by the movement of said rotary arm.

3. In combination, a movable switch-arm, a switch adapted to be operated by the movement of said movable arm, an electric circuit connected at one end to the said movable arm, a resistance connected at one end to one end of said circuit and at the other end to said switch, a second resistance connected at a point near its middle to said switch, and a series of contacts connected to said resistances and adapted to be engaged by said movable arm.

4c. In combination, a rotary switch-arm, a switch adapted to be operated by the movement of said rotary arm, an electric circuit connected at one end to said rotary arm, a resistance connected at one end to one end of said circuit and at the other end to said switch, a second resistance connected at a point near its middle to said switch, and a circular row of contacts connected to said resistances and adapted to be engaged by said rotary arm.

5. In combination, an electric circuit, two variable resistances connected to said contacts, one of said resistances being connected to one end of said electric circuit, a movable switch-arm connected to the other end of said circuit and adapted to connect variable portions of said resistances in series with said circuit, and a switch adapted to be operated by the movement of said movable arm and to connect one of said resistances in series with a portion of the other of said resistances.

6. In combination,two variable resistances, an electric circuit, and a switch adapted to connect step by step one of said resistances in series with said circuit, then to cutout a portion of said resistance and to connect the second resistance in shunt to said circuit, and then to transfer step by step the said second resistance from shunt to series relation to said circuit.

Signed at Pittsfield, ll/Iassacl1usctts,this 31st day of March, 1903.

LEONARD WILSON.

Witnesses:

L. S. HAWKINS, R. E. HAYNES. 

